1. Field of the Invention
The present invention relates to a seat belt system for restraining an occupant of a vehicle. In particular, the present invention relates to the tensioning of seat belt webbing about the occupant during an emergency situation, such as a collision.
2. Description of the Prior Art
An automotive vehicle is typically equipped with a seat belt that restrains movement of the occupant during an emergency situation, such as a collision. To restrain movement of the occupant effectively, the seat belt webbing should be tight against the occupant. Systems which pull the seat belt tight against the occupant during an emergency situation are known.
An example of such a system is shown in U.S. Pat. No. 4,423,846. U.S. Pat. No. 4,423,846 discloses a seat belt retractor having a spool on which seat belt webbing is wound. The spool is supported for rotation in belt withdrawal and belt retraction directions. A drum is connectable with and rotatable with the spool. An end portion of a cable is connected to the drum and is wound onto the drum. The other end portion of the cable is connected to a relatively large mass, such as the vehicle's engine, which is movable relative to the vehicle under certain circumstances. For example, during a head-on collision, the engine will break loose from the vehicle frame, upon deceleration of the vehicle at a rate above a predetermined rate, and move forward relative to the vehicle frame. The movement of the engine causes the cable to rotate the drum, thereby rotating the retractor spool in the belt retraction direction to tighten the seat belt webbing against the occupant.
In an alternate embodiment disclosed in U.S. Pat. No. 4,423,846, the other end portion of the cable is connected to a piston in a chamber of a pyrotechnic device, rather than to the engine. Upon sensing the occurrence of an emergency situation, such as a collision, gas generating material is ignited and the piston moves within the chamber due to the expanding gases. This pulls the cable to rotate the drum, thereby rotating the retractor spool in the belt retraction direction to tighten the seat belt webbing against the occupant.
U.S. Pat. No. 4,597,545 discloses another seat belt tensioning system. In U.S. Pat. No. 4,597,545, a retractor is slidably connected to the vehicle. One end of a cable is connected to the retractor. The cable is trained about pulleys and its other end is connected to the front bumper of the vehicle. The front bumper moves inwardly relative to the vehicle during a head-on collision. This inward movement of the front bumper tensions the cable, which in turn slides the retractor relative to the vehicle to tension the belt webbing against an occupant.